DOUBLE-BLIND, PLACEBO-CONTROLLED INVESTIGATION OF THE EFFECT OF COMBINED PHOTOTHERAPY LOW-INTENSITY LASER THERAPY UPON EXPERIMENTAL ISCHEMIC PAIN IN HUMANS

Background and Objective: This study assessed the putative analgesic e ffect of combined monochromatic light/laser irradiation at low intensi ty (660-950 nm; 31.9 J/cm(2): pulsed at 16 or 73 Hz). Study Design/Mat erials and Methods: The investigation was completed under double-blind conditions using a standardised form of the submaximal effort tourniq uet technique. Healthy male volunteers naive to the experimental condi tions (n = 45) attended on two occasions for the purposes of pain indu ction, the first during which baseline data were obtained and on a sec ond occasion during which they were randomly allocated to one of two t reatments or a placebo condition. For the treatment conditions, irradi ation was applied to the ipsilateral Erb's point at the parameters sta ted; for the placebo condition, sham ''irradiation'' was delivered usi ng a dummy unit. Pain was measured using computerised visual analogue scales and McGill Pain Questionnaires (MPQ) to assess ''current pain i ntensity'' and ''worst pain experienced,'' respectively. Results: Anal ysis of variance and appropriate post hoc tests demonstrated only a we ak (but significant) hypoalgesic effect compared to placebo (P < 0.05) in the treatment group irradiated at 16Hz for the sensory component o f the MPQ; other comparisons were found to be nonsignificant. Conclusi ons: These results do not provide convincing evidence for the hypoalge sic potential of combined monochromatic light/laser irradiation, at le ast at the parameters used here, and thus indicate the necessity of ad ditional work to investigate this modality further in order to assess the potential benefit, if any, of such treatment in the clinical setti ng. (C) 1995 Wiley-Liss, Inc.